A flash device is essentially an electrically erasable programmable read only memory (EEPROM or E2PROM), which allow blocks of data to be programmed or erased at relatively high operating speeds. A flash differs from an EEPROM in that a flash is generally adapted to operate on blocks of data while an EEPROM or E2PROM has to be erased all at once, even though the EEPROM may be programmed on a byte-by-byte basis.
Today, NAND flash and NOR flash memory devices dominate the non-volatile flash memory market. A NAND flash memory is a non-linear addressed device requiring multiplexed input/output (I/O) pins for handling both data and commands. A NAND flash memory device is a serially interfaced device in which address, data, and control information are multiplexed on the same pins. As a result of its serial interface, the NAND flash memory device requires more complex and extensive I/O interfaces and drivers for handling the multiplexed I/O pins. A NAND flash memory device is typically accessed in bursts, thereby permitting, for example, 512 bytes of data to be written to or read from the device. However, random access errors generated by physical defects in the geometry of the NAND gates results in low reliability for NAND flash memory devices.
A NOR flash device is a linear addressed device, which comprises separate address and data lines. In this regard, a NOR flash device is somewhat similar to a dynamic random access memory (DRAM) device. A NOR flash memory generally comprises sufficient address pins that allows it to be memory mapped into a processor's address space, thereby allowing the NOR flash to be accessed like a read only memory (ROM). The cell structure of NAND flash is almost one-half the size of a NOR flash's cell structure and as a result, for a given die, NAND flash memory devices have a much higher packing density than NOR flash memory devices. For example, NOR flash capacities range from 1 megabyte (MB) to 4 MBs while NAND flash capacities range from 32 MBs to 512 MBs. In addition to its higher packing density and thus higher capacity, NAND flash is cheaper than NOR flash since it is much cheaper to produce. NOR flash memory devices also possess less than 10% of the lifespan of NAND flash memory devices.
Given today's trends in wireless communication technologies, consumer demand is constantly forcing device manufactures to create access devices such as handhelds, which store more data using less chip real estate at significantly lower costs. A NAND flash memory is typically utilized in cell phones because of its low cost and low power consumption compared with traditional NOR flash memory. In cellular telephones (cell phones) and personal digital assistant (PDA) type devices, for example, NAND flash may be utilized to store digitized images and data. In some instances, NAND flash memory devices may also be utilized to store computer instructions or code, which is to be executed by one or more processors in an access device such as a cellular telephone or PDA. Although NAND flash possesses much higher bit densities, is inexpensive, and has much lower power consumption than NOR flash, it also has a very low reliability due to bad blocks and prolonged access time. These issues of reliability and access time make it more difficult to execute the computer instructions directly from the NAND flash. NOR flash is not suitable for execution of instructions because of its small capacity and shorter lifespan.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.